F# Actor is an actor library. The actor programming model is inherently concurrent, an actor is a primitive that wraps a computation, the computation is ran by sending messages to the actor.
The actor can then respond to the reciept of the message by executing one or more of the following actions (possibly concurrently),

Create a number of new actors

Send a another message to other actors

Change the behaviour to be used upon reciept of the next message.

Currently there are a couple of actor libraries on the .NET platform

AkkaDotNet - This is a port of the scala based actor framework Akka. This is written in C# but does have an F# API.

Orleans - This is a Microsoft research project aiming to simplfy the development of scalable cloud based services, with a high level of abstraction over the actor programming model.

F# Core - The FSharp.Core library actually has its own actor implementation in the form of the MailboxProcessor<'T> type.

F# Actor in no way aims to be a clone of either of these however it does draw on the ideas in all of the above frameworks as well as Erlang and OTP. Instead F# actor aims to be as simple and safe to use as possible hopefully
making it difficult for you to shoot yourself in the foot.

The library comes with comprehensible documentation.
It can include a tutorials automatically generated from *.fsx files in the content folder.
The API reference is automatically generated from Markdown comments in the library implementation.

The project is hosted on GitHub where you can report issues, fork
the project and submit pull requests. If you're adding new public API, please also
consider adding samples that can be turned into a documentation. You might
also want to read library design notes to understand how it works.

The library is available under Public Domain license, which allows modification and
redistribution for both commercial and non-commercial purposes. For more information see the
License file in the GitHub repository.